Brian Carmichael, age 9, of Visalia, California, for his question:

 What makes the knots in knotty pine?

Slices of knotty pine are cut from certain evergreen trees that have dark brown pine cones and dark green needles. They fill the air with a fresh, tangy fragrance. And the smell is related to the dark knots in the pale wood. It comes from gummy resin, which is inside the needles and twigs and trunk. When a pine tree is injured, sticky resin oozes out and seals the wound. Later the gob of resin sets very hard and turns dark.

A young pine looks like a pointed Christmas tree, with low, wide branches brushing the ground. As it grows taller, it sheds its lower boughs and adds more at the top of the trunk. When the low branches fall off, they leave wounds in the trunk. And the resin oozes in to seal them. Later, the tree adds rings of pale new wood around its trunk and the gobs of hard resin are buried inside. They are the dark knots we see in slices of knotty pine.